Search

Avian nest design varies depending on environmental factors but may also be influenced by between‐species interactions. In the brood parasitism context, hosts may evolve nest architectures that may limit parasite access to the nest cup, reduce parasite laying success or hinder parasite chick success. Therefore, nest characteristics may reduce the likelihood or minimise the costs of being parasitised. The common redstart Phoenicurus phoenicurus is a regular host of the common cuckoo Cuculus canorus, for which cuckoo eggs are often laid outside the nest cup, resulting in low effective parasitism rates. This allowed us to evaluate variation in host nest design and test whether nest design characteristics correlate with brood parasitism likelihood and cuckoo laying success (i.e. cuckoo egg laid in the nest cup versus outside the nest cup). While recording brood parasitism events in two distant redstart populations, we documented nest cup characteristics, such as internal dimensions, materials used and nest cup position, along with the nest‐box dimensions. Cuckoo parasitism likelihood was lower for redstart nests in cavities with smaller entrances, for redstart nests with smaller nest cups and with nest cups that were built level to the rim material. For parasitised nests, cuckoo laying success was lower at redstart nests with nest cups placed further from the cavity entrance. Our results suggest a conditional process, where the cavity entrance size first prevents brood parasites access, then the cup size and the cup level in reference to the rim material affect the cuckoo choice, and finally, the nest cup position hinders cuckoo's laying success. The use of multiple nest design strategies may explain the current low effective parasitism rates in this system. Host nest design may serve as a frontline defence that could shape parasite's preferences, and consequently host nest characteristics. [ABSTRACT FROM AUTHOR]

Urbanization reflects a major form of environmental change impacting wild birds globally. Whereas urban habitats may provide increased availability of water, some food items, and reduced predation levels compared to rural, they can also present novel stressors including increased light at night, ambient noise, and reduced nutrient availability. Urbanization can also alter levels of brood parasitism, with some host species experiencing elevated levels of brood parasitism in urban areas compared to rural areas. Though the demographic and behavioral consequences of urbanization and brood parasitism have received considerable attention, their consequences for cellular‐level processes are less understood. Telomeres provide an opportunity to understand the cellular consequences of different environments as they are a well‐established metric of biological state that can be associated with residual lifespan, disease risk, and behavior, and are known to be sensitive to environmental conditions. Here we examine the relationships between urbanization, brood parasitism, and blood telomere lengths in adult and nestling song sparrows Melospiza melodia. Song sparrows are a North American songbird found in both urban and rural habitats that experience high rates of brood parasitism by brown‐headed cowbirds Molothrus ater in the urban, but not the rural, sites in our study system. Among adults and nestlings from non‐parasitized nests, we found no differences in relative telomere lengths between urban and rural habitats. However, among urban nestlings, the presence of a brood parasite in the nest was associated with significantly shorter relative telomere lengths compared to when a brood parasite was absent. Our results suggest a novel, indirect, impact of urbanization on nestling songbirds through the physiological impacts of brood parasitism. [ABSTRACT FROM AUTHOR]

Brood parasites are expected to lay only one egg per parasitized nest, as the existence of several parasitic nestlings in a brood increases competition and can lead the starvation of some of them. However, multiparasitism (laying of two or more eggs by one or more parasitic females in a single host nest) is surprisingly frequent. Here, we study multiparasitism by different females or by the same female (repeated parasitism) in the great spotted cuckoo Clamator glandarius, a non‐evictor brood parasite that mainly parasitizes the magpie Pica pica, and whose chicks may be raised together with host nestlings in the same nest. We used a total of 262 magpie nests found during four breeding seasons. Multiparasitism and repeated parasitism are very frequent because this brood parasite is less virulent than other cuckoo species and magpie hosts can successfully raise more than one parasitic nestling per nest. The total number of cuckoo chicks fledged was higher in multiparasitized nests than in single‐ or double‐parasitized magpie nests. Magpie breeding success (i.e. the proportion of eggs that produce young that leave the nest) did not differ between single‐, double‐, and multiparasitized magpie nests. These results suggest that multiparasitism is an adaptation in the great spotted cuckoo. The intensity of parasitism (number of cuckoo eggs per nest), after controlling for the potential effect of year, did not affect nest desertion or nest predation rate, neither during the incubation nor the nestling periods. This implies that nest concealment does not affect the susceptibility of one nest being parasitized and predated, as nest predation rate was similar regardless of the intensity of parasitism. Predation rate during the nestling phase did not vary according to intensity of parasitism, which does not support either the 'mutualism' hypothesis or the 'predation cost of begging' hypothesis. [ABSTRACT FROM AUTHOR]

Parental care is a costly behaviour that raises the prospects of offspring survival. In species with biparental care these costs are shared by both parents, although there may be a conflict regarding the relative investment of each sex. Avian brood parasites leave all the costs of rearing offspring to their hosts. The magnitude of these costs and their consequences on the relative role of both sexes in parental care and future reproduction remain mostly unknown. Here, we investigate whether provisioning rate of nestlings by magpie hosts Pica pica differs between broods parasitized by the great spotted cuckoo Clamator glandarius and non‐parasitized broods, and whether the relative contribution of each sex to provisioning is affected by parasitism. Furthermore, we explore the effect of parasitism on magpie's future reproduction. We found that provisioning rate was similar in parasitized and non‐parasitized broods, and that the relative contribution of males and females was also similar, irrespectively of the parasitism status. However, rearing parasitic offspring seems to have a negative long‐term effect on magpie's breeding phenology in the following breeding season. Our results suggest that, although brood parasitism by great spotted cuckoos does not seem to influence the relative contribution of both sexes to parental care, it may entail long‐term extra costs in terms of breeding delay for magpies. [ABSTRACT FROM AUTHOR]

Breeding ground food availability is critical to the survival and productivity of adult birds. The common cuckoo Cuculus canorus is a brood‐parasitic Afro‐Palearctic migrant bird exhibiting long‐term (breeding) population declines in many European countries. Variation in population trend between regions and habitats suggests breeding ground drivers such as adult food supply. However, cuckoo diet has not been studied in detail since before the most significant population declines in Europe began in the mid‐1980s. 20th century studies of cuckoo diet largely comprised field observations likely to carry bias towards larger prey taxa. Here we demonstrate the potential value of 1) using high‐throughput DNA sequencing of invertebrate prey in faeces to determine cuckoo diet with minimal bias towards large prey taxa, and 2) using crowd‐sourced digital photographs from across Britain to identify lepidopteran cuckoo prey taxa during recent years post‐decline (2005–2016). DNA analysis found a high frequency of Lepidoptera, including moths of family Lasiocampidae, prominent within the past literature, but also grasshoppers (Orthoptera) and flies (Diptera) that may be overlooked by field observation methodologies. The range of larval lepidopteran prey identified from photographs largely agreed with those previously documented, with potential signs of reduced diversity, and identities of key adult prey taxa were supported by molecular results. Notably, many identified cuckoo prey taxa have shown severe declines due to agricultural intensification, suggesting this has driven spatial patterns of cuckoo loss. Landscape‐scale, lowland rewilding interventions provide opportunities to understand the scale of reversal of previous agricultural intensification that may be necessary to restore prey populations sufficiently to permit recolonization by cuckoos. [ABSTRACT FROM AUTHOR]

Avian obligate brood parasites do not provide parental care for their eggs and young, and may therefore serve as a strong model system to test predictions of evolutionary sex‐allocation theories, independent of parental modulation of primary sex ratios. However, none of the handful of previous studies examining offspring sex ratio in brood parasitic birds have revealed a bias from parity at the level of the female parasite, the host species or temporal scale(s). This is also surprising, because in at least one brood parasite, the brown‐headed cowbird Molothrus ater, adult sex ratios are consistently and heavily male‐biased. Here we used a large database of embryonic and nestling cowbirds' genetic sex ratios collected from nests of a single host species, the prothonotary warbler Protonotaria citrea to assess potential overall, temporal and individual patterns of bias. Contrary to previous findings, we documented an increase in the calculated male sex ratios later in the breeding season. There was no effect of whether embryos or nestlings were sampled, implying a lack of host parental effect on shifting the primary‐to‐secondary sex ratios of brood parasitic offspring. Future work should explore the sex‐specific survival and recruitment pattern of fledgling cowbirds raised by this and other host species to reconcile theoretical and empirical predictions and patterns. [ABSTRACT FROM AUTHOR]

Animals rely on an array of environmental triggers or cues to make their behavioural and life‐history decisions. Brood–parasitic females should prefer the best host to maximize their reproductive success. Despite the fact that Eurasian reed warbler Acrocephalus scirpaceus is one of the most frequent host of the common cuckoo Cuculus canorus, parasitic chicks often prematurely fall out of the nests and drown. To establish whether these events are influenced by the size of the nest, we experimentally replaced original Eurasian reed warbler nests for much bigger great reed warbler Acrocephalus arundinaceus ones and transferred cuckoo chicks into them to record their fate. The chicks in bigger nests showed significantly lower falling‐out rate (4 of 29) compared with those remained in smaller nests (12 of 32). These findings suggest that host nest size plays an important role in the suitability of host species and that smaller host nests may pose a high mortality risk to the relatively big cuckoo chicks. Moreover, cuckoo chicks that fell out of the nests were significantly less fed by foster parents before falling‐out event than those stayed in the nests. This indicates that insufficient parental care may also facilitate falling‐out of cuckoo chicks, probably because hungry chicks are more restless in host nests. The relatively frequent falling‐out events represent a substantial and underestimated cost of brood parasites. Without video surveillance it can incorrectly be confused with predation. We therefore strongly recommend using video‐recording for determining predation costs in birds. [ABSTRACT FROM AUTHOR]

Parent decisions about food allocation are usually based on simple time-saving rules that optimize their own fitness; however, they can sometimes vary depending on the prevailing ecological conditions both outside and inside the nest. Parent-offspring interactions also become more complex when parents suffer from brood parasitism, which implies that they care for the parasite's eggs and unrelated young. The great spotted cuckoo Clamator glandarius is a specialist brood parasite that uses the magpie Pica pica as its primary host. Here, by filming food allocation by magpie parents in natural non-parasitized and experimentally parasitized and non-parasitized magpie nests, we have found that magpie provisioning behaviour is highly complex including two types of feedings apart from normal ones. First, false feedings, when the parent touched the chick's beak but did not leave any food, occurred more frequently when feeding a cuckoo than when feeding magpie nestlings. Second, two types of what we have called coax feedings: 2a) when magpie parents induce a nestling to beg by waking it up by touching it softly with the beak, and 2b) when parents disregard begging signals (always from brood parasitic great spotted cuckoos) while coaxing one non-begging nestling (always one of their own) to feed it. We suggest that brood parasitism, involving selfish excessively begging nestlings, could have acted as a selective pressure for both false and coax feedings to evolve, as both imply ignoring nestlings that beg too much. We also discuss that these parental responses could have evolved either by a discrimination without recognition mechanism, or, more probably, by a recognition-based discrimination mechanism. [ABSTRACT FROM AUTHOR]

When brood parasites exploit multiple host species, egg rejection by hosts may select for the evolution of host-specific races, where each race mimics a particular host's egg type. However, some brood parasites that exploit multiple hosts with the ability to reject foreign eggs appear to have only a single egg type. In these cases, it is unclear how the parasite egg escapes detection by its hosts. Three possible explanations are: 1) host-specific races are present, but differences in egg morphology are difficult for the human eye to detect; 2) the brood parasite evolves a single egg type that is intermediate in appearance between the eggs of its hosts; 3) or the parasite evolves mimicry of one of its hosts, which subsequently allows it to exploit other species with similar egg morphology. Here we test these possibilities by quantifying parameters of egg appearance of the brood-parasitic Pacific koel Eudynamys orientalis and seven of its hosts. Koel eggs laid in the nests of different hosts did not show significant differences in colour or pattern, suggesting that koels have not evolved host-specific races. Koel eggs were similar in colour, luminance and pattern to the majority of hosts, but were significantly more similar in colour and luminance to one of the major hosts than to two other major hosts, supporting hypothesis 3. Our findings suggest that mimicry of one host can allow a brood parasite to exploit new hosts with similar egg morphologies, which could inhibit the evolution of host defences in naïve hosts. [ABSTRACT FROM AUTHOR]

Conspecific brood parasites lay eggs in nests of other females of the same species. A variety of methods have been developed and used to detect conspecific brood parasitism (CBP). Traditional methods may be inaccurate in detecting CBP and in revealing its true frequency. On the other hand more accurate molecular methods are expensive and time consuming. Eadie developed a method for revealing CBP based on differences in egg morphology. That method is based on Euclidean distances calculated for pairs of eggs within a clutch using standardized egg measurements (length, width and weight). We tested the applicability of this method in the common pochard Aythya ferina using nests that were identified as parasitized (39 nests) or non-parasitized (16 nests) based on protein fingerprinting of eggs. We also analyzed whether we can distinguish between parasitic and host eggs in the nest. We found that variation in MED can be explained by parasitism but there was a huge overlap in MED between parasitized and non-parasitized nests. MED also increased with clutch size. Using discriminant function analysis (DFA) we found that only 76.4% of nests were correctly assigned as parasitized or non-parasitized and only 68.3% of eggs as parasitic or host eggs. Moreover we found that MED in parasitized nests increased with relatedness of the females that laid eggs in the nest. This finding was supported by positive correlation between MED and estimated relatedness in female-female pairs. Although variation in egg morphology is associated with CBP, it does not provide a reliable clue for distinguishing parasitized nests from non-parasitized nests in common pochard. [ABSTRACT FROM AUTHOR]

Coevolutionary theories of brood parasite strategy and host defense have been informed by research on egg mimicry and host recognition. However, there is no information on the strategies of New World parasitic cuckoos and their hosts. The striped cuckoo Tapera naevia is a New World cuckoo that uses multiple host species and maintains an egg color polymorphism. To investigate if color-matching influenced rejection behavior in hosts, I conducted an egg rejection experiment on a host that lays blue-green eggs, the rufous-and-white wren Thryophilus rufalbus and a host that lays white eggs, the plain wren Cantorchilus modestus. I used spectrophotometric analysis of egg color to determine the degree of egg color-matching. I found that at the field site the striped cuckoo lays highly mimetic eggs for the rufous-and-white wren, in both color and brightness. The rufous-and-white wren was more likely to accept mimetic artificial eggs than non-mimetic eggs. The plain wren exhibited low rejection rates for both mimetic and non-mimetic artificial eggs. The evidence from this study indicates that the striped cuckoo lays eggs that are closely color-matched to those of its preferred host, the rufous-and-white wren, and that this mimicry improves acceptance. [ABSTRACT FROM AUTHOR]

How do potential hosts escape detrimental interactions with brood parasites? Current consensus is that hole-nesting and granivorous birds avoid brood parasites, like common cuckoos Cuculus canorus, by their inaccessible nest-sites and food unsuitable for parasites, respectively. Any open-nesting insectivorous hosts are believed to remain open to brood parasite exploitation which leads to the evolution of costly host defences like egg or chick discrimination. In contrast to this coevolutionary scenario, we show for the first time that a previously not studied but seemingly suitable host species escapes brood parasites. The Asian verditer flycatcher Eumyias thalassinus, feed newly hatched chicks entirely with beetles and grasshoppers. These are poor quality and hard to digest diet items that are rarely fed to own or cuckoo chicks by regular hosts. Indeed, chick cross-fostering experiments showed that these food items remained undigested by either cuckoos or other sympatric passerines causing them to die quickly. Egg discrimination experiments showed that the flycatcher accepts any foreign eggs. Although most but not all other potential explanations can be safely excluded at present, the most parsimonious historical explanation for these patterns is that the flycatcher exploits a trophic niche that no other sympatric bird can exploit, and that any cuckoo lineages that switch from their original hosts to the flycatcher have no possibilities for establishing viable populations. Thus, the current classification of host suitability based on diet composition may need revision, raising an important cautionary tale for comparative studies and the interpretation of apparent host rejection of parasitic chicks. [ABSTRACT FROM AUTHOR]

Traditionally it was thought that the arms race between brood parasites and their hosts was confined to the egg stage of the breeding cycle because many host species are able to reject mimetic parasitic eggs but they are unable to reject strongly different parasitic chicks. However, recently, new cases of chick rejection, discrimination, or mimicry, have been published confirming the possibility that an equivalent arms race to that found at the egg stage could ever be played out at the chick stage. Here, I review the evidence for the existence of a co-evolutionary arms race at the nestling stage. Recent findings include new deceiving strategies used by brood parasitic chicks, defensive strategies used by foster parents and adaptive strategies of host nestlings. This review shows that both chick discrimination and relationships between brood parasites and their hosts at the nestling stage are much more complicated than previously believed. At least in some brood parasite-host systems, an arms race at the nestling stage is working. [ABSTRACT FROM AUTHOR]

Identifying the natal origins of brood parasites is a major challenge that usually requires labor-intensive searching for nests of host species. Stable isotope analysis of feathers and other body tissues of parasitic young could be a possible tool for determining natal origins if tissues reflect the isotopic composition of the diet fed to nestlings. We measured the carbon (13C) and nitrogen (15N) isotope compositions of feathers for two age-classes of brown-headed cowbirds Molothrus ater at the Konza Prairie Biological Station near Manhattan, Kansas: nestlings raised by five species of songbird hosts in two different habitats, and juveniles captured after independence. Isotope values from cowbird nestlings did not differ among host species and we were unable to assign juvenile cowbirds to their natal hosts. However, nestlings raised in grassland habitat had feathers that contained significantly higher δ13C values and lower δ15N values than nestlings raised in shrub habitats. In addition, independent juveniles had isotopic signatures that were similar to cowbird nestlings raised on shrub habitats. Although dickcissel Spiza americana comprised the majority of samples from shrub habitats, our conclusions reflect the natural pattern of parasitism at the site and should be representative of cowbirds raised at Konza. We conclude that stable isotope analysis of feathers is effective for determining the natal origins of parasitic young if isotope values from nestlings are isotopically distinct among habitats. [ABSTRACT FROM AUTHOR]

In broods of great egrets Ardea alba and other birds with siblicidal nestlings, the first-hatched brood members generally secure far more food than do their juniors. This feeding advantage could be caused by parental favoritism, or by seniors attacking and thereby dominating their juniors. We investigated these possibilities by comparing how fathers and mothers allocated food among their offspring when chicks were free to fight versus when they were physically separated by a Plexiglas barrier. When free to fight, dominant nestlings received significantly more food than did their subordinates. When nestlings were separated, mothers, but not fathers, delivered significantly more food per meal to the β (second-ranked) chick than to other nestlings. This is the first experimental evidence of differential feeding by parents in a species with aggressive nestlings. [ABSTRACT FROM AUTHOR]

Intraspecific brood parasites lay their eggs in the nests of conspecifics. There are a number of methods for detecting intraspecific brood parasitism (IBP) in birds based on egg morphology. Here we test method, which calculates the Euclidean distances between eggs in a given clutch in a three-dimensional space (weight, length and width). A parasitised clutch is predicted to contain an egg (or eggs) that is significantly different from the clutch's other eggs. Data from three species were analysed. Our captive zebra finch Taeniopygia guttata clutches did not include any instances of IBP, the wild jackdaw Corvus monedula data were unlikely to contain any, and for the goldeneye Bucephala clangula data set we had an observational estimate of IBP. We simulated IBP in the zebra finch, jackdaw and goldeneye data to test whether the method reliably detects an experimentally ‘parasitised’ clutch. We show that the distributions of the test statistics greatly overlap in ‘parasitised’ and unmodified clutches, and are dependent on the clutch size. We therefore conclude that the method can only be used with caution, after calibrating it for a given population. [ABSTRACT FROM AUTHOR]

Nestling parasites typically beg more intensively than do host nestlings yet these exaggerated displays are also honest in that they are modulated by hunger and age. We hypothesized that honesty was also maintained in the food solicitation behaviors of fledgling brood parasites because the benefits and costs of their begging displays are similar to those of nestling parasites. Begging displays of hand-reared 14–32 days old brown-headed cowbirds Molothrus ater that had experimentally manipulated nutritional needs were recorded to analyze variation in the peak frequency, duration, and rate of fledglings’ begging bouts. Peak frequency of bouts decreased with greater age and was lower for females. Bout rate was greater with increasing hunger levels of fledgling parasites but did not vary with age. Consistent and predictable variation of acoustic begging displays with age, sex, and hunger-level indicates honesty in host-parasite communication systems through conveying truthful information about the many possible needs of parasitic fledglings. [ABSTRACT FROM AUTHOR]

Proposes that the existence of imperfect adaptations in brood parasites and their hosts could reflect age-dependent territory and nest-site selection patterns of the host among bird species. Nest-site constraints; Example in the reed warbler Acrocephalus scirpaceus.

Obligate avian brood parasites lay stronger eggs than their hosts or non‐parasitic relatives because they are rounder and have a thicker eggshell. Additionally, some other characteristics of the brood parasitic eggshells related to their microstructure such as size and orientation of calcite crystal units could also contribute to generating even stronger shells. An eggshell microstructure formed by small randomly oriented calcite crystal units can increase the robustness of the eggshells of birds. Here, the eggshell microstructure of avian brood parasites as well as their hosts have been characterized in detail, using X‐ray diffraction analyses to estimate the size and degree of orientation of calcite crystal units making the eggshell. Specifically, the brood parasitic great spotted cuckoo Clamator glandarius and two hosts (jackdaws Corvus monedula and magpie Pica pica) and one non‐host species (the pigeon, Columba livia domestica) were considered. Calcite crystal of the eggshell of the brood parasitic species was smaller and more randomly oriented than those of the eggshells of non‐parasitic species, which suggest that eggshell microstructure would contribute to explain why parasitic eggs are more resistant to breakage than those of their hosts. [ABSTRACT FROM AUTHOR]